JPH04280873A - Production of firebrick - Google Patents

Abstract

PURPOSE:To omit a drying process and save energy in processes for producing firebricks, especially unburned firebricks. CONSTITUTION:A refractory raw material comprising alumina or magnesium oxide is mixed with >=2wt.% of a raw material containing conductive particles and a binder, followed by molding the mixture. The molded product is brought into contact with two electrodes, and an electric current is directly applied to the electrodes to thermally cure and/or dry the molded product, thereby permitting to reduce the cost of energy into approximately a half thereof and to especially perfectly automatize the production processes of firebricks in the case of the firebricks or unburned firebricks.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing firebricks, which includes a step of quickly and efficiently heat-curing and/or drying a molded body.

0002

[Prior Art] In the conventional method for manufacturing firebricks, for example, mixed clay to which a binder has been added is molded using a hydraulic press, friction press, etc., and the wet molded body is made of heavy oil or kerosene as an energy source. A method is used in which the material is heated in a drying oven or a portion on the entrance side of a tunnel kiln, dried, and then fired.

In this case, it is of course necessary to secure a drying oven or a long tunnel kiln with a drying section, as well as securing a place to store the wet bricks and reloading the wet bricks onto pallets for drying. , it is necessary to carry the bricks to the drying oven, and when drying thick bricks, it is necessary to hold them in the drying oven for a considerable length of time so that the heat penetrates to the inside of the refractory bricks. In addition to a lot of heat loss from the furnace walls, the gas discharged from the furnace carries away a lot of heat energy, so the efficiency of energy use is low and a surprisingly large amount of fuel is consumed.

[0004] There are other methods for drying bricks, such as using steam or hot air, but their energy efficiency is about the same as the drying oven described above. Regarding the drying method of wet ceramic bases, please refer to the ``Electric Drying Apparatus for Ceramic Bases'' published in Japanese Patent Publication No. 37-18690.
discloses the use of electrical heating to dry an insulator base.

[0005] In this way, when the material to be dried is directly heated by electricity, the internal temperature of the ceramic material can be raised more quickly than in other methods, and it is a type of ceramic material. Thermal efficiency is also good in drying the insulator base, and it has the effect of being able to dry more quickly.

[0006] However, energization takes advantage of the presence of a relatively small amount of alkali ions and water added as deflocculants, etc., and in order to ensure heat resistance and insulation, a large amount of alkali ions must be added. This is undesirable, and in most cases, as the drying progresses, the electrical resistance becomes very large, reaching 100%.
It was necessary to apply a high voltage exceeding 0V, and there was a risk of electric shock.

[0007] Other methods include microwave heating and far-infrared rays, which are not suitable for drying very thick items, but have good thermal efficiency, can pass heat to a certain depth, and can dry quickly. It is used in the manufacturing process of ceramics.

[0008]

Problem to be Solved by the Invention The present invention provides a process for manufacturing firebricks that includes a drying process that can be carried out with less manpower and fewer steps, is safe, and can reduce energy consumption and equipment costs. The present invention aims to provide a method for manufacturing.

[0009]

[Means for Solving the Problems] The present invention has been made to achieve the above-mentioned problems, and the method for manufacturing a refractory brick of the present invention includes adding 2% by weight or more of conductive particles to a refractory raw material made of an oxide. and further add a binder to form a mixed clay, bring an electrode into contact with a molded body made of the mixed clay, and heat the molded body to harden and/or dry it by passing electricity directly into the molded body. It is characterized by

[0010] In a preferred embodiment of the method for producing a refractory brick of the present invention, the binder contains a thermosetting resin. In another preferred embodiment of the method for producing a refractory brick of the present invention, the conductive particles are graphite and the thermosetting resin is a phenol resin.

In another preferred embodiment of the method for producing refractory bricks of the present invention, the refractory raw material is magnesia clinker or alumina clinker. In another preferred embodiment of the method for producing a refractory brick of the present invention, the forming is performed using a mechanical press. In another preferred embodiment of the method for producing a refractory brick of the present invention,
The refractory is an unfired refractory.

[0012] Refractory raw materials made of oxides, which are the main constituents of refractory bricks, are insulating materials in most cases, and for this reason, the refractory materials of the present invention that combine only oxide refractory raw materials cannot be used. Manufacturing methods cannot be applied.

[0013] The present invention is a method for producing a refractory brick containing conductive particles such as graphite particles and non-oxide compound particles, in which 2% by weight of the total amount of refractory raw material and conductive particles is used.
By containing the above-mentioned conductive particles, at least after being formed into a molded product, the molded product has a relatively low electrical resistance and can be heated by direct current supply. This means that a power supply of several hundred volts or less can be used, which does not require any special equipment and can be handled by simply switching the voltage using a transformer.

[0014] In the case of graphite, the blending amount of the conductive particles is usually 30% by weight or less in order to obtain appropriate properties for the refractory brick, but when using granular conductive particles that do not exhibit significant cleavage. In some cases, the content may be 30 to 90% by weight.

[0015] Examples of conductive particles made of non-oxide compounds include silicon carbide (SiC) and boron carbide (B4C).
, particles containing zirconium boride (ZrB2) as a main component, and aluminum metal powder, which turns into fire-resistant alumina at high temperatures, can also be used as conductive particles.

[0016] As a binder, if it is normally used in the manufacture of firebricks, it may be water-soluble such as water glass or polyvinyl alcohol, or it may be a binder containing an organic solvent such as an acrylic binder. It can be used even if there is.

[0017] Various methods can be used to form firebricks, such as pour molding, compaction molding, hand molding, press molding, etc. However, since drying is normally required in the production of bricks, there are molding methods that require less added moisture; In particular, it is preferable to use a press molding method. Moreover, when using the press molding method, it is possible to easily secure a flat surface on which electricity can be applied by applying an electrode to the molded refractory brick.

[0018] When electricity is applied directly to the formed refractory brick, it is necessary to make good electrical contact between the electrode and the refractory brick, and it is recommended to use a plate-shaped electrode to increase the contact area. is preferred. Any metal material can be used as the material for the electrode, and copper, which has good conductivity, is particularly preferred.

As a method of applying electricity, for example, a plate-shaped electrode plate is placed inside the mold, the molding is performed in that state, and the mold is removed from the mold, or the mold is insulated to prevent electrical short-circuiting. Then, it is also possible to conduct electricity inside the mold. Since current heating only heats the object to be heated, the surface that radiates heat to the outside is small and there is little heat loss to the surroundings, so almost all of the thermal energy converted from electrical energy is effectively used to heat the refractory bricks. . Furthermore, since the applied voltage does not need to be very high, there is less risk of electric shock.

In the method for producing refractory bricks of the present invention, since the conductive particles mixed in take charge of most of the conductivity of the refractory brick, there is no need to add a binder or peptizer containing alkali ions, and it is not necessary to add a binder or peptizer containing an alkali ion. It can also be preferably applied when using a dissolved organic binder.

[0021] If a thermosetting resin is used as a binder,
When producing unfired bricks, the final product can be obtained by heating and hardening, which further reduces energy consumption. As a thermosetting resin, it is relatively cheap, has a large amount of residual carbon after pyrolysis, and the residual carbon develops bond strength, and the amount of pyrolyzed organic matter released when used at high temperatures is small. It is preferred to use phenolic resins from.

When the conductive particles are graphite, the graphite particles have a flat particle shape due to their cleavage property, and have good conductivity in the direction parallel to the flat plates, which makes them fire resistant. Even if the brick contains only a relatively small amount of conductive particles, it is advantageous because it provides sufficient conductivity to directly energize the refractory brick.

As the refractory raw material consisting of an oxide coexisting with the carbon component converted from graphite or thermosetting resin, magnesia clinker or alumina clinker, which does not react with the carbon component up to high temperatures and has high heat resistance, is suitable.

[0024] The method for producing refractory bricks of the present invention can be used for producing both fired and unfired bricks, but in the production of unfired bricks, the final product can be obtained by simply heating with electricity directly. For example, a plate-shaped electrode is sandwiched between press-formed bricks, and they are heated and energized one after another on a line (it is also possible to heat and harden many bricks at the same time by connecting them in parallel and energizing them). This makes it possible to change the drying process in the brick manufacturing process, which normally could only be done in a batch process, to a continuous automated process, and for unfired bricks, the entire manufacturing process can be automated. is possible.

[0025]Depending on the type of binder used, it may be preferable to perform press molding in a heated state, and by incorporating an appropriate insulating material into the press, it is also possible to perform direct electrical heating during pressing. In addition, when transferring the formed bricks to the drying oven, the work of transferring the bricks to a drying pallet can be omitted, and unlike when drying in a drying oven, the degree of heat distribution depending on the position in the drying oven can be eliminated. Considering that the drying oven which requires land and equipment costs can be omitted, and the energy savings and process time are also taken into account, the industrial application effect of the method for manufacturing refractory bricks of the present invention is extremely high. This is noticeable.

[0026]

EXAMPLES The present invention will now be explained in more detail by way of examples. Example 1 The method for producing a refractory brick of the present invention was applied to the production of a magnesia carbon brick, which is a typical unfired refractory brick.

[0027] That is, 80% by weight of magnesia clinker with a particle size of 3 mm or less and a particle size of 1.5 mm.
Put the following 20% by weight of flaky graphite into a universal mixer,
In addition to this, the non-volatile content of resol-based phenolic resin is 75% by weight.
Add 3% by weight of methanol solution and mix.
Standard bricks measuring 5 mm x 114 mm x 230 mm were press-molded at a pressure of 250 kg/cm2.

[0028] The brick formed in this way has a size of 65 mm×
Place a copper electrode plate on the 114 mm surface and place it with the 65 mm x 230 mm surface facing down on an insulated vise.
Further, the electrode plate was sandwiched between wooden boards having flat surfaces so as to make good contact with the bricks, and then tightened with a vise so that a load of about 20 kg was applied. In addition, a thermocouple was previously attached to the surface of the refractory brick.

When AC voltage was applied to the raw refractory brick (molded body) in this state via a transformer, a current of approximately 430 A (approximately 17 kW) flowed at a voltage of 39.4 V, and the surface temperature rose to 104 kW in approximately 1 minute. It has become ℃. Thereafter, electricity was applied for another minute under the same conditions (the surface temperature had reached 170°C), and then the electricity was turned off.

[0030] The compressive strength of this refractory brick at room temperature before and after electric heating is measured in a cut-out piece of 65 mm x 50 mm x 50 m.
When examined using a test piece of green brick, the result was 11.
The weight of the test piece after heat curing was 131.4 kg/cm2, which was 5 kg/cm2.

Example 2 As another example of an unfired brick, a similar test was conducted on an alumina brick containing 3% by weight of flaky graphite. That is, 87% by weight of alumina clinker with a particle size of 3.33 mm or less, 10% by weight of fine magnesia powder, and 3% by weight of flaky graphite with a particle size of 1.5 mm or less were placed in a universal mixer. 3% by weight of a methanol solution of resol type phenol resin with a nonvolatile content of 75% by weight was added to the mixture and mixed, and a regular brick of 65 mm x 114 mm x 230 mm was press-molded at 250 kg/cm2.

[0032] Next, 230 mm x
Place the electrode plate on a 114 mm surface, place it with the 65 mm x 230 mm surface facing down on an insulated vise, then sandwich it between wooden boards so that the electrode plate is in good contact with the brick, and apply a load of approximately 60 kg in the vise. I tightened it so that it would fit. When AC voltage was applied to the raw brick in this state via a transformer, a current of approximately 19.1 A (approximately 5.3 kW) flowed at a voltage of 278 V, and the surface temperature of the brick rose to 100 °C in approximately 5 minutes. became. Immediately after that, the power was turned off.

[0033] The compressive strength of this refractory brick at room temperature before and after electrical heating was examined using a cut-out 65 mm x 50 mm x 50 mm test piece, and it was found that the raw brick test piece had a compression strength of 8.2 kg/
cm2, but the test piece after heat curing was 131
．． It was 1 kg/cm2. When we calculated the energy efficiency based on the above experiments, we obtained the following results.

The amount of energy required for drying and curing is approximately 90 liters of heavy oil per 1 ton of refractory brick for any unfired refractory brick in the case of a conventional drying oven that uses heavy oil as fuel, which is approximately This corresponds to a calorific value of 850,500 kcal.

Regarding the magnesia carbon unfired brick of Example 1, assuming that curing is completed by heating at 100° C., power consumption is 32 kWh per ton, and 45.7 kWh at a power factor of 70%. . This amount of electricity is 3
This corresponds to a calorific value of 9302 kcal.

That is, even if the efficiency (usually about 40%) of converting fossil fuels into electrical energy is taken into account, significant energy savings are possible. On the other hand, when the same calculation was made for alumina unfired bricks, it was found that 71.4kWh
of electricity is consumed, and this electricity amount is 61404 kca
Since it corresponds to the amount of heat of 1, the same conclusion was reached.

[0037] The price of heavy oil is 31.35 per liter.
If we calculate the price in Japanese yen and assume that the price of electricity is 22 yen per kWh, we have calculated that the energy cost will be about half that.

[0038]

[Effects of the Invention] By carrying out the method for manufacturing refractory bricks of the present invention, the drying time in the drying step of the refractory brick manufacturing process can be shortened, and at the same time, the molded refractory bricks can be transferred to pallets or transported. It has been confirmed that the amount of work required for drying can be reduced, and the amount of energy and energy costs used for drying can be significantly reduced.

[0039] Furthermore, the drying oven, which requires land and equipment costs, can be replaced with a more compact and inexpensive transformer, and by using electrical energy, it is possible to reduce the amount of SOX and NOX emissions. Furthermore, when the refractory bricks are unfired bricks, it has become possible to continuously and automate the refractory brick manufacturing process, including inspection.

Claims (6)

[Claims] Claim 1: Adding 2% by weight or more of conductive particles to a refractory raw material made of an oxide, and further adding a binder to form a mixed clay, molding the mixed clay, and contacting an electrode to the obtained molded body. 1. A method for producing a refractory brick, which comprises curing and/or drying the molded product by heating the molded product by applying electricity directly to the molded product. 2. The method for producing a firebrick according to claim 1, wherein the binder contains a thermosetting resin. 3. The method for producing a firebrick according to claim 2, wherein the conductive particles are graphite and the thermosetting resin is a phenolic resin. 4. The method for producing a refractory brick according to claim 1, wherein the refractory raw material made of an oxide is magnesia clinker or alumina clinker. 5. The method for producing a refractory brick according to claim 1, wherein the forming is performed using a mechanical press. 6. The method for producing a refractory brick according to claim 2, wherein the refractory brick is an unfired refractory brick.